Ceramic complex and method for producing the same

ABSTRACT

A method for producing a ceramic complex includes: preparing a raw material mixture that contains 5% by mass or more and 40% by mass or less of first rare earth aluminate fluorescent material particles containing an activating element and a first rare earth element different from the activating element, 0.1% by mass or more and 32% by mass or less of oxide particles containing a second rare earth element, and the balance of aluminum oxide particles, relative to 100% by mass of the total amount of the first rare earth aluminate fluorescent material particles, the oxide particles, and the aluminum oxide particles; preparing a molded body of the raw material mixture; and obtaining a sintered body by calcining the molded body in a temperature range of 1,550° C. or higher and 1,800° C. or lower.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims priority to Japanese Patent Application No.2020-113289, filed on Jun. 30, 2020, the disclosure of which is herebyincorporated by reference in its entirety.

BACKGROUND Technical Field

The present disclosure relates to a ceramic complex and a method forproducing the same.

Description of Related Art

There is known a light emitting device comprising a light emitting diode(LED) or a laser diode (LD) and a wavelength conversion member includinga fluorescent material for converting the wavelength of light emittedfrom a light emitting element such as an LED or LD. Such a lightemitting device is used for applications such as on-vehicle lighting,general-purpose lighting, backlight of liquid crystal display devices,and light sources for projectors. In this specification, the“fluorescent material” is used in the same meaning as a “fluorescentphosphor”.

For example, Japanese Unexamined Patent Publication No. 2015-149394discloses a ceramic complex including a Ce-activated yttrium aluminumgarnet fluorescent material, an inorganic material composed of aluminumoxide existing between fluorescent material particles, and additiveparticles having a particle diameter smaller than that of thefluorescent material particles adhered to cover at least a part of thesurface of the fluorescent material particles.

Ceramic complexes including a fluorescent material and a translucentinorganic material are required to have even higher luminance.

Thus, an aspect of the present disclosure has an object to provide aceramic complex with high luminance and a method for producing the same.

SUMMARY

A first embodiment of the present disclosure is a method for producing aceramic complex including: preparing a raw material mixture thatcontains first rare earth aluminate fluorescent material particlescontaining an activating element and a first rare earth elementdifferent from the activating element, oxide particles containing asecond rare earth element, and aluminum oxide particles, wherein acontent of the first rare earth aluminate fluorescent material particlesis in a range of 5% by mass or more and 40% by mass or less, a contentof the oxide particles containing the second rare earth element is in arange of 0.1% by mass or more and 32% by mass or less, and a content ofthe aluminum oxide particles is the balance, relative to 100% by mass ofa total amount of the first rare earth aluminate fluorescent materialparticles, the oxide particles containing the second rare earth element,and the aluminum oxide particles; preparing a molded body by molding theraw material mixture; and obtaining a sintered body by calcining themolded body in a temperature range of 1,550° C. or higher and 1,800° C.or lower.

A second embodiment of the present disclosure is a ceramic complexincluding a first crystal phase that contains a first rare earthaluminate fluorescent material containing an activating element and afirst rare earth element different from the activating element, a secondcrystal phase composed of a second rare earth aluminate containing asecond rare earth element, wherein a content of an element capable ofbeing an activator in the second crystal phase is 200 ppm by mass orless, and a third crystal phase composed of aluminum oxide, wherein acontent of the first crystal phase is in a range of 5% by volume or moreand 45% by volume or less, a content of the second crystal phase is in arange of 0.5% by volume or more and 50% by volume or less, and a contentof the third crystal phase is the balance, relative to 100% by volume ofa total amount of the first crystal phase, the second crystal phase, andthe third crystal phase.

In accordance with the embodiments of the present disclosure, a ceramiccomplex with high luminance and a method for producing the same can beprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a flowchart describing a method for producing a ceramiccomplex according to the present disclosure.

FIG. 1B is a flowchart describing a method for producing a ceramiccomplex according to the present disclosure.

FIG. 2A is a flowchart describing a method for producing a ceramiccomplex according to the present disclosure.

FIG. 2B is a flowchart describing a method for producing a ceramiccomplex according to the present disclosure.

FIG. 3A is a schematic plan view of a light emitting device according tothe present disclosure.

FIG. 3B is a schematic cross-sectional view of a light emitting deviceaccording to the present disclosure.

FIG. 4 is a graph describing a relationship between the content (% bymass) of oxide particles contained in a raw material mixture and therelative luminance of a ceramic complex according to the presentdisclosure.

FIG. 5 is a scanning electron microscope (SEM) photograph of a secondaryelectron image in a cross section of a ceramic complex according toExample 3.

FIG. 6 is an SEM photograph of a reflected electron image in a crosssection of the ceramic complex according to Example 3.

DETAILED DESCRIPTION

The ceramic complex and the method for producing the same will behereunder described on the basis of embodiments. The embodimentsdescribed below are exemplifications for embodying the technical idea ofthe present disclosure, and the present disclosure is not limited to thefollowing ceramic complex and the method for producing the same. Therelationships between color names and chromaticity coordinates, and therelationships between wavelength ranges of light and color names ofmonochromic light are in accordance with Japanese Industrial Standard(JIS) Z8110. In the present specification, ceramics refers to anyinorganic non-metallic material at a temperature of 1,000° C. or lower.

Method for Producing Ceramic Complex

The method for producing a ceramic complex comprises: preparing a rawmaterial mixture that contains first rare earth aluminate fluorescentmaterial particles containing an activating element and a first rareearth element different from the activating element, oxide particlescontaining a second rare earth element, and aluminum oxide particles,wherein the content of the first rare earth aluminate fluorescentmaterial particles is in a range of 5% by mass or more and 40% by massor less, the content of the oxide particles is in a range of 0.1% bymass or more and 32% by mass or less, and the content of the aluminumoxide particles is the balance, relative to 100% by mass of the totalamount of the first rare earth aluminate fluorescent material particles,the oxide particles, and the aluminum oxide particles; preparing amolded body by molding the raw material mixture; and obtaining asintered body by calcining the prepared molded body in a temperaturerange of 1,550° C. or higher and 1,800° C. or lower.

It is presumed that the aluminum oxide in the molded body obtained bymolding the raw material mixture undergoes particle growth by mergingparticles by the heat during calcining in the temperature range of1,550° C. or higher and 1,800° C. or lower, and along with the particlegrowth, the oxide particles containing a second rare earth elementgather around the aluminum oxide, and the oxide particles react with thealuminum oxide particles to form a second rare earth aluminate. When thesecond rare earth aluminate is formed around the first rare earthaluminate fluorescent material particles, the first rare earth aluminatefluorescent material and the second rare earth aluminate can be easilyintegrated without forming a grain boundary, thereby forming a firstcrystal phase containing the first rare earth aluminate fluorescentmaterial. Since the first rare earth aluminate fluorescent materialparticles contained in the molded body and the second rare earthaluminate formed by reacting the oxide particles containing a secondrare earth element with the aluminum oxide particles are integrated, thefirst crystal phase containing the first rare earth aluminatefluorescent material contained in the ceramic complex has a large firstcrystal diameter G1. When the first crystal diameter G1 of the firstcrystal phase containing the first rare earth aluminate fluorescentmaterial becomes large, the first rare earth aluminate fluorescentmaterial can easily absorb the light emitted from the excitation lightsource and emit light with high luminance. The first crystal phasecontaining the first rare earth aluminate fluorescent material containsan activating element, a first rare earth element different from theactivating element, and a second rare earth element derived from theoxide particles. The first rare earth element and the second rare earthelement may be the same element or different elements.

For example, the aforementioned Japanese Unexamined Patent PublicationNo. 2015-149394 discloses a ceramic complex in which additive particlessubstantially not containing an activator are attached to the surface offluorescent material particles. In this ceramic complex, the fluorescentmaterial particles and the additive particles are not integrated, andthere is an interface between the fluorescent material particles and theadditive particles.

On the other hand, in the first crystal phase contained in the ceramiccomplex according to the embodiment of the present disclosure, aninterface is hardly formed between the first rare earth aluminatefluorescent material and the second rare earth aluminate. Therefore, thelight emitted from the first rare earth aluminate fluorescent materialin the ceramic complex is less affected by reflection due to thedifference in refractive index near the interface, and the first crystalphase having a large first crystal diameter G1 increases the absorptionefficiency of the light emitted from the excitation light source,allowing the ceramic complex to emit wavelength-converted light withhigh luminance. In the ceramic complex, the reason why there is nointerface in the first crystal phase where the first rare earthaluminate fluorescent material and the second rare earth aluminate areintegrated is presumed as follows. By calcination in the temperaturerange of 1,550° C. or higher and 1,800° C. or lower, the aluminum oxidereacts with the oxide particles while growing particles to form a secondrare earth aluminate, and the second rare earth aluminate reacts with afirst rare earth aluminate fluorescent material having a similarcomposition. Therefore, the interface is hardly formed between the firstrare earth aluminate fluorescent material and the second rare earthaluminate, and the both are easily integrated and formed into one firstcrystal phase.

The resulting ceramic complex also contains a second crystal phasecomposed of a second rare earth aluminate formed by reacting thealuminum oxide particles which grow particles by the heat duringcalcining, with the oxide particles. This second rare earth aluminate isnot integrated with the first rare earth aluminate fluorescent material.The resulting ceramic complex also contains a third crystal phasecomposed of aluminum oxide, which grows particles by the heat duringcalcining and does not react with the oxide particles. There is aninterface between the first crystal phase in which the first rare earthaluminate fluorescent material and the second rare earth aluminate areintegrated and the third crystal phase composed of aluminum oxide in theceramic complex, since the crystal structure of each crystal phase isdifferent. There is also an interface between the second crystal phasecomposed of the second rare earth aluminate and the third crystal phasecomposed of aluminum oxide, since the crystal structure of each crystalphase is different. When the second rare earth aluminate formed byreacting the oxide particles containing a second rare earth element withthe aluminum oxide particles approaches the first rare earth aluminatefluorescent material, the second rare earth aluminate and the first rareearth aluminate fluorescent material are integrated, and thus the thirdcrystal phase composed of aluminum oxide is present between the secondcrystal phase composed of the second rare earth aluminate and the firstcrystal phase containing the first rare earth aluminate fluorescentmaterial. In the ceramic complex containing the first crystal phasecontaining the first rare earth aluminate fluorescent material, thesecond crystal phase composed of the second rare earth aluminate, andthe third crystal phase composed of aluminum oxide, the light isscattered by the interface formed between each crystal phase, the lightabsorption efficiency of the first crystal phase containing the firstrare earth aluminate fluorescent material integrated with the secondrare earth aluminate is increased, and the wavelength of the light isefficiently converted, so that light with high luminance can be emitted.

FIGS. 1A and 1B, and FIGS. 2A and 2B are flowcharts showing examples ofthe method for producing a ceramic complex. Steps of the method forproducing a ceramic complex will be described with reference to thedrawings. As shown in FIG. 1A, the method for producing a ceramiccomplex includes a step S101 of preparing a raw material mixturecontaining first rare earth aluminate fluorescent material particles,oxide particles containing a second rare earth element, and aluminumoxide particles, a step S102 of preparing a molded body by molding theraw material mixture, and a step S103 of obtaining a sintered body bycalcining the molded body in a temperature range of 1,550° C. or higherand 1,800° C. or lower. As shown in FIG. 2A, the method for producing aceramic complex includes a step S201 of preparing a raw materialmixture, and a step S202 of preparing a molded body by molding the rawmaterial mixture; and may include a step S203 of obtaining a firstsintered body by primarily calcining the molded body in a temperaturerange of 1,550° C. or higher and 1,800° C. or lower, and a step S204 ofobtaining a second sintered body by secondarily calcining the firstsintered body in a temperature range of 1,500° C. or higher and 1,800°C. or lower by hot isostatic pressing (HIP). As shown in FIG. 1B or FIG.2B, the method for producing a ceramic complex may optionally include anannealing treatment step S104 or S205 after the step S103 of obtaining asintered body, the step S203 of obtaining a first sintered body, or thestep S204 of obtaining a second sintered body. Further, the method forproducing a ceramic complex may optionally include a processing stepS105 or S206 of cutting the obtained sintered body or the secondsintered body into a desired size or thickness after the step S103 ofobtaining a sintered body or the step S204 of obtaining a secondsintered body, and may further optionally include a surface treatmentstep S106 or S207.

Step of Obtaining Raw Material Mixture

First Rare Earth Aluminate Fluorescent Material Particles

The first rare earth aluminate fluorescent material particles preferablyhave a first rare earth aluminate composition that contains at least onefirst rare earth element Ln¹ selected from the group consisting of Y,Lu, Gd, and Tb, Ce serving as the activating element, and Al, and mayoptionally contain Ga, in which the total molar ratio of the first rareearth element Ln¹ and Ce is 3; the molar ratio of Ce is the product of aparameter a in a range of more than 0 and 0.22 or less, and 3; the totalmolar ratio of Al and Ga is in a range of 4.5 or more and 5.5 or less;the molar ratio of Al is the product of a parameter c in a range of morethan 0 and 1.1 or less, and 5; and the molar ratio of Ga that may beoptionally contained is the product of a parameter b in a range of 0 ormore and 0.4 or less, and 5.

In the step of preparing a raw material mixture, the first rare earthaluminate fluorescent material particles preferably have a compositionrepresented by the following formula (I);(Ln¹ _(1-a)Ce_(a))₃(Al_(c)Ga_(b))₅O₁₂  (I)

wherein Ln¹ represents at least one element selected from the groupconsisting of Y, Gd, Lu, and Tb; and the parameters a, b, and c eachsatisfy 0<a≤0.22, 0≤b≤0.4, 0<c≤1.1, and 0.9≤b+c≤1.1.

The first rare earth element Ln¹ contained in the first rare earthaluminate fluorescent material particles may include two or moreelements selected from the group consisting of Y, Lu, Gd, and Tb. Thefirst rare earth element Ln¹ may include at least one selected from thegroup consisting of Y, Lu, and Gd. The first rare earth element Ln¹ mayinclude Y and Gd, or may include Y and Lu. When two or more first rareearth elements Ln¹ are contained in the first rare earth aluminatefluorescent material and the first rare earth elements Ln¹ are Y and Gd,the molar ratio of Y and Gd (Y:Gd) is preferably in a range of 99.5:0.5to 70:30, and may be in a range of 99:1 to 80:20, or may be in a rangeof 99:1 to 90:10 in the composition of the first rare earth aluminatefluorescent material.

In the composition of the first rare earth aluminate fluorescentmaterial particles, the molar ratio of Ce is represented by the productof 3 and the parameter a. In the composition of the first rare earthaluminate fluorescent material particles, the molar ratio of Ce ispreferably in a range of more than 0 and 0.66 or less, and may be in arange of 0.001 or more and 0.60 or less, may be in a range of 0.003 ormore and 0.450 or less, may be in a range of 0.006 or more and 0.300 orless, may be in a range of 0.012 or more and 0.270 or less, or may be ina range of 0.015 or more and 0.240 or less. In the composition of thefirst rare earth aluminate fluorescent material particles, the parametera is in a range of more than 0 and 0.22 or less (0<a≤0.22), and may bein a range of 0.0003 or more and 0.20 or less (0.0003≤a≤0.20), may be ina range of 0.001 or more and 0.150 or less (0.001≤a≤0.150), may be in arange of 0.002 or more and 0.100 or less (0.002≤a≤0.100), may be in arange of 0.004 or more and 0.090 or less (0.004≤a≤0.090), or may be in arange of 0.005 or more and 0.080 or less (0.005≤a≤0.080).

In the composition of the first rare earth aluminate fluorescentmaterial particles, the molar ratio of Al is represented by the productof 5 and the parameter c. In the composition of the first rare earthaluminate fluorescent material particles, the molar ratio of Al is in arange of more than 0 and 5.5 or less, and may be in a range of 0.54 ormore and 5.0 or less, or may be in a range of 0.63 or more and 5.0 orless. In the composition of the first rare earth aluminate fluorescentmaterial particles, the parameter c is in a range of more than 0 and 1.1or less, and may be in a range of 0.6 or more and 1.0 or less(0.6≤c≤1.0), or may be in a range of 0.7 or more and 1.0 or less(0.7≤c≤1.0).

In the composition of the first rare earth aluminate fluorescentmaterial particles, Ga may not be contained. In the composition of thefirst rare earth aluminate fluorescent material particles, the molarratio of Ga is represented by the product of 5 and the parameter b. Inthe composition of the first rare earth aluminate fluorescent materialparticles, the molar ratio of Ga is in a range of 0 or more and 2.0 orless, and may be in a range of 0.1 or more and 1.5 or less, or may be ina range of 0.2 or more and 1.2 or less. In the composition of the firstrare earth aluminate fluorescent material particles, the parameter b isin a range of 0 or more and 0.4 or less (0≤b≤0.4), and may be in a rangeof 0.02 or more and 0.3 or less (0.02≤b≤0.3), or may be in a range of0.04 or more and 0.24 or less (0.04≤b≤0.24).

In the composition of the first rare earth aluminate fluorescentmaterial particles, the total molar ratio of Al and Ga is in a range of4.5 or more and 5.5 or less, and may be 5. In the composition of thefirst rare earth aluminate fluorescent material particles, the sum ofthe parameter b and the parameter c is in a range of 0.9 or more and 1.1or less (0.9≤b+c≤1.1), and may be 1 (b+c=1).

The first rare earth aluminate fluorescent material particles preferablyhave a first average particle diameter D1, as measured according to aFisher Sub-Sieve Sizer (hereinafter, also referred to as “FSSS”) method,in a range of 4 μm or more and 40 μm or less, more preferably in a rangeof 5 μm or more and 35 μm or less, and even more preferably in a rangeof 8 μm or more and 30 μm or less. The FSSS method is a type of an airpermeability method, and is a method for measuring a specific surfacearea by utilizing the flow resistance of air so as to mainly determinean average particle diameter of primary particles. The average particlediameter measured according to the FSSS method is a Fisher Sub-SieveSizer's number. When the first average particle diameter D1 of the firstrare earth aluminate fluorescent material particles, as measuredaccording to the FSSS method, falls within the range of 4 μm or more and40 μm or less, the first crystal diameter G1 of the first crystal phasecontaining the first rare earth aluminate fluorescent materialintegrated with the second rare earth aluminate becomes larger in theresulting ceramic complex. In the resulting ceramic complex, the firstcrystal phase having a larger first crystal diameter G1 can efficientlyabsorb the light emitted from the excitation light source to convert thewavelength, thereby emitting light with high luminance. Further, whenthe first average particle diameter D1 of the first rare earth aluminatefluorescent material particles falls within the range of 4 μm or moreand 40 μm or less, the formation of voids is suppressed, and a ceramiccomplex having a high relative density can be obtained together with theoxide particles containing a second rare earth element and the aluminumoxide particles.

Oxide Particles Containing Second Rare Earth Element

The oxide particles containing a second rare earth element may be simplyreferred to as “oxide particles”. The second rare earth elementcontained in the oxide particles is preferably an element different fromthe activating element contained in the first rare earth aluminatefluorescent material. Examples of the second rare earth elementcontained in the oxide particles include at least one selected from thegroup consisting of Sc, Y, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er,Tm, Yb, and Lu. The second rare earth element contained in the oxideparticles is preferably at least one selected from the group consistingof Y, La, Nd, Pm, Gd, Tb, Dy, Ho, Er, Yb, and Lu, and more preferably atleast one selected from the group consisting of Y, La, Nd, Gd, Tb, Yb,and Lu. It is further preferred that the oxide particles contain atleast one second rare earth element Ln² selected from the groupconsisting of Y, Gd, Tb, and Lu. The oxide particles may be two or moretypes of oxide particles containing one type of the second rare earthelement and different second rare earth elements. Specifically, theoxide particles are preferably particles composed of at least one oxideselected from the group consisting of Y₂O₃, La₂O₃, Pr₇O₁₁, Nd₂O₃, Gd₂O₃,Tb₄O₇, Yb₂O₃, and Lu₂O₃. It is more preferred that the oxide particlesare at least one type of oxide particles selected from the groupconsisting of Y₂O₃, La₂O₃, Nd₂O₃, Gd₂O₃, Tb₄O₇, Yb₂O₃, and Lu₂O₃, andeven more preferred that the oxide particles are at least one type ofoxide particles selected from the group consisting of Y₂O₃, Gd₂O₃,Tb₄O₇, and Lu₂O₃. One type of oxide particles may be used alone, or twoor more types thereof may be used in combination. The oxide particlesrefer to particles composed of oxides containing a second rare earthelement. The oxide particles may not contain aluminum. The oxideparticles without containing aluminum refer to oxide particles having analuminum content of less than 1% by mass.

The oxide particles preferably have a second average particle diameterD2, as measured according to the FSSS method, in a range of 0.05 μm ormore and less than 5 μm, and more preferably in a range of 0.1 μm ormore and 4 μm or less. When the second average particle diameter D2 ofthe oxide particles falls within the range of 0.05 μm or more and lessthan 5 μm, in calcining a molded body to be described later in a rangeof 1,550° C. or higher and 1,800° C. or lower, the oxide particleseasily gather around the aluminum oxide that grows particles by the heatduring calcining, and the oxide particles containing a second rare earthelement react with the oxide aluminum to easily form a second rare earthaluminate. The formed second rare earth aluminate can be integrated withthe first rare earth aluminate fluorescent material to increase thefirst crystal diameter G1 of the first crystal phase containing thefirst rare earth aluminate fluorescent material, and the light emittedfrom the excitation light source can be easily wavelength-converted,thereby producing a ceramic complex capable of emitting light with highluminance.

Aluminum Oxide Particles

The aluminum oxide particles preferably have an aluminum oxide purity of99.0% by mass or more, and more preferably 99.5% by mass or more. Whenthe aluminum oxide purity in the aluminum oxide particles is 90.0% bymass or more, impurities can be reduced, and a ceramic complex capableof emitting light with high luminance can be produced. The aluminumoxide purity in the aluminum oxide particles can be referred to thevalue of aluminum oxide purity listed in the catalog. In the case wherethe aluminum oxide purity in the aluminum oxide particles is unknown,the purity of the aluminum oxide particles can be measured in such amanner that the mass of the aluminum oxide particles is measured, thealuminum oxide particles are then calcined at 800° C. for 1 hour in anair atmosphere to eliminate organic materials or moisture attached to oradsorbed on the aluminum oxide particles, the mass of the aluminum oxideparticles after calcination is measured, and the mass of the aluminumoxide particles after calcination is divided by the mass of the aluminumoxide particles before calcination.

The aluminum oxide particles preferably have a third average particlediameter D3, as measured according to the FSSS method, in a range of 0.1μm or more and 1.5 μm or less, and more preferably in a range of 0.2 μmor more and 1.0 μm or less. When the third average particle diameter D3of the aluminum oxide particles falls within the range of 0.1 μm or moreand 1.5 μm or less, in calcining a molded body to be described later ina range of 1,550° C. or higher and 1,800° C. or lower, the aluminumoxide particles easily grow by the heat during calcining to form asecond rare earth aluminate together with the oxide particles, therelative density is increased, and the light emitted from the excitationlight source can be easily wavelength-converted, thereby producing aceramic complex capable of emitting light with high luminance.

Raw Material Mixture

In the raw material mixture, the content of the first rare earthaluminate fluorescent material particles is in a range of 5% by mass ormore and 40% by mass or less, the content of the oxide particles is in arange of 0.1% by mass or more and 32% by mass or less, and the contentof the aluminum oxide particles is the balance, relative to 100% by massof the total amount of the first rare earth aluminate fluorescentmaterial particles, the oxide particles, and the aluminum oxideparticles. When the content of the first rare earth aluminatefluorescent material particles falls within the range of 5% by mass ormore and 40% by mass or less relative to 100% by mass of the totalamount of the first rare earth aluminate fluorescent material particles,the oxide particles, and the aluminum oxide particles in the rawmaterial mixture, it is preferred that the content of the oxideparticles is in a range of 0.5% by mass or more and 30% by mass or lessand the content of the aluminum oxide particles is the balance; it ismore preferred that the content of the oxide particles is in a range of1.0% by mass or more and 28% by mass or less and the content of thealuminum oxide particles is the balance; it is further preferred thatthe content of the oxide particles is in a range of 3.0% by mass or moreand 25% by mass or less and the content of the aluminum oxide particlesis the balance; and it is particularly preferred that the content of theoxide particles is in a range of 5.0% by mass or more and 20% by mass orless and the content of the aluminum oxide particles is the balance.When the content of each of the first rare earth aluminate fluorescentmaterial particles, the oxide particles, and the aluminum oxideparticles in the raw material mixture falls within the above-mentionedrange, the oxide particles and the aluminum oxide particles are reactedeach other to form a second rare earth aluminate by calcination in thetemperature range of 1,550° C. or more and 1,800° C. as described later,and the second rare earth aluminate can be integrated with the firstrare earth aluminate fluorescent material to produce a ceramic complexcontaining a first crystal phase having a large first crystal diameterG1. Further, when the content of each of the first rare earth aluminatefluorescent material particles, the oxide particles, and the aluminumoxide particles in the raw material mixture falls within theabove-mentioned range, a ceramic complex containing a third crystalphase composed of aluminum oxide in which the aluminum oxide particlesgrow and a second crystal phase composed of a second rare earthaluminate which is not integrated with the first rare earth aluminatefluorescent material by reacting the aluminum oxide particles with theoxide particles, can be produced.

The first rare earth aluminate fluorescent material particles, the oxideparticles, and the aluminum oxide particles can be mixed in a wet or drymanner using a mixer to obtain a raw material mixture. As the mixer, aball mill, a vibration mill, a roll mill, a jet mill, or the like, whichare industrially commonly used, can be used.

Step of Preparing Molded Body

In the step of preparing a molded body, the raw material mixture ismolded to prepare a molded body. As the method for forming the moldedbody, a known method such as a press molding method can be adopted.Examples of the press molding method include a die press molding methodand a cold isostatic pressing (CIP) method for which the term is definedin No. 2109 of JIS Z2500:2000. Alternatively, the raw material mixturemay be uniaxially compressed and molded to obtain a molded body. As themethod for molding the raw material mixture to obtain a molded body, twokinds of methods may be adopted to shape the molded body, for example,CIP may be performed after die press molding, or CIP may be performedafter uniaxial compression by a roller bench method. For CIP, it ispreferable to press the molded body by a cold isostatic pressing methodusing water as a medium.

The pressure during die press molding or when molding by uniaxialcompression is preferably in a range of 5 MPa or more and 50 MPa orless, and more preferably in a range of 5 MPa or more and 30 MPa orless. When the pressure during die press molding or when molding byuniaxial compression falls within the above-mentioned range, the moldedbody can be shaped to a desired shape.

The pressure in CIP is preferably in a range of 50 MPa or more and 200MPa or less, and more preferably in a range of 50 MPa or more and 180MPa or less. When the pressure in CIP falls within the range of 50 MPaor more and 200 MPa or less, it is possible to form a molded bodycapable of obtaining a ceramic complex having a relative density of 95%or more by calcining at 1,550° C. or higher and 1,800° C. or lower, asdescribed later.

Step of Obtaining Sintered Body by Calcining (Primary Calcining Step)

In the step of obtaining a sintered body, the molded body is calcined ina temperature range of 1,550° C. or higher and 1,800° C. or lower toobtain a sintered body. The molded body may be primarily calcined in atemperature range of 1,550° C. or higher and 1,800° C. or lower toobtain a first sintered body. The calcining temperature is preferably ina range of 1,600° C. or higher and 1,750° C. or lower, and morepreferably in a temperature range of 1,650° C. or higher and 1,700° C.or lower. When the calcining temperature of the molded body falls withinthe range of 1,550° C. or higher and 1,800° C. or lower, the reactionbetween the aluminum oxide particles and the oxide particles can bepromoted without dissolving the first rare earth aluminate fluorescentmaterial to produce a ceramic complex containing a first crystal phasewith a large crystal diameter containing the first rare earth aluminatefluorescent material integrated with the second rare earth aluminate, asecond crystal phase composed of the second rare earth aluminate, and athird crystal phase composed of the aluminum oxide.

Secondary Calcining Step

The secondary calcining step is a step of obtaining a second sinteredbody by secondarily calcining the first sintered body in a temperaturerange of 1,500° C. or higher and 1,800° C. or lower by hot isostaticpressing (HIP). The method for producing a ceramic complex may includethe secondary calcining step.

In the secondary calcining step, the secondary calcining is preferablyperformed in a temperature range of 1,500° C. or higher and 1,800° C. orlower by hot isostatic pressing (HIP) for which the term is defined inNo. 2112 of JIS Z2500:2000. By performing the secondary calcining step,a ceramic complex with higher relative density can be obtained. Thesecondary calcining temperature is more preferably in a range of 1,550°C. or higher and 1,800° C. or lower, even more preferably in atemperature range of 1,600° C. or higher and 1,750° C. or lower, andparticularly preferably in a temperature range of 1,650° C. or higherand 1,700° C. or lower. The secondary calcining can be performed in anargon or nitrogen atmosphere.

In the secondary calcining, the pressure in HIP is preferably in a rangeof 50 MPa or more and 300 MPa or less, and more preferably in a range of80 MPa or more and 200 MPa or less. When the pressure in HIP fallswithin the range of 50 MPa or more and 300 MPa or less, the entiresecond sintered body can be made uniform and of higher density withoutdamaging the crystal structure of the first crystal phase containing thefirst rare earth aluminate fluorescent material.

The time of the secondary calcining performed by HIP is, for example, ina range of 0.5 hour or more and 20 hours or less, and preferably in arange of 1 hour or more and 10 hours or less in order to uniformlyincrease the density of the entire second sintered body.

Annealing Treatment

The obtained sintered body, the first sintered body, or the secondsintered body may be subjected to an annealing treatment in a reducingatmosphere. By annealing the obtained sintered body in a reducingatmosphere, the oxidized activating element contained in the firstcrystal phase containing the first rare earth aluminate fluorescentmaterial can be reduced, and the decrease in wavelength conversionefficiency and luminance due to oxidation of the activating element thatis the center of light emission can be suppressed. The reducingatmosphere may be an atmosphere containing at least one rare gasselected from the group consisting of helium, neon, and argon, or anitrogen gas, and a hydrogen gas or a carbon monoxide gas, and it ispreferred that at least argon or a nitrogen gas, and a hydrogen gas or acarbon monoxide gas are contained in the atmosphere. The annealingtreatment may be performed on the sintered body or the first sinteredbody, may be performed on the second sintered body, or may be performedon either the first sintered body or the second sintered body.

The annealing treatment temperature is a temperature lower than thecalcining temperature, and is preferably in a range of 1,000° C. orhigher and 1, 500° C. or lower. The annealing treatment temperature ismore preferably in a range of 1,000° C. or higher and 1,400° C. orlower, and even more preferably in a range of 1,100° C. or higher and1,350° C. or lower. When the annealing treatment temperature is atemperature lower than the calcining temperature, primary calciningtemperature, or secondary calcining temperature, and falls within therange of 1,000° C. or higher and 1,500° C. or lower, the oxidizedactivating element contained in the first crystal phase containing thefirst rare earth aluminate fluorescent material in the ceramic complexcan be reduced, and the decrease in wavelength conversion efficiency andluminance can be suppressed.

Processing Step

The obtained sintered body may be processed to be cut into a desiredsize or thickness. A known cutting method can be used, and examplesthereof include a cutting method using at least one method selected fromblade dicing, laser dicing, and wire sawing. Of these, wire sawing ispreferred since the unevenness of the cut surface can be furtherreduced.

Surface Treatment Step

Further, a surface treatment step described below may be added. Thesurface treatment step is a step of surface-treating the surface of thecut product obtained by cutting the obtained sintered body or the secondsintered body. The surface treatment step not only allows the surface ofthe ceramic complex to be in an appropriate state in order to improvethe light emitting characteristics of the ceramic complex, but alsoallows the ceramic complex to be formed into a desired shape, size, orthickness in combination with the above-mentioned processing step oralone. The surface treatment step may be performed before the processingstep in which the sintered body or the second sintered body is cut intoa desired size or thickness, or may be performed after the processingstep. Examples of the surface treatment method include at least onemethod selected from a sandblasting method, a mechanical grindingmethod, a dicing method, and a chemical etching method.

The resulting ceramic complex preferably contains a second crystal phasecomposed of a second rare earth aluminate, wherein a content of anelement capable of being an activator in the second crystal phase is 200ppm by mass or less. The oxide particles contained in the raw materialmixture react with the aluminum oxide to form a second rare earthaluminate, and the formed second rare earth aluminate is integrated withthe first rare earth aluminate fluorescent material to form a firstcrystal phase. Also, the oxide particles contained in the raw materialmixture react with the aluminum oxide to form a second rare earthaluminate, and the formed second rare earth aluminate is not integratedwith the first rare earth aluminate fluorescent material to form asecond crystal phase composed of the second rare earth aluminate. Thesecond crystal phase composed of the second rare earth aluminate in theceramic complex is a second crystal phase formed by reacting the oxideparticles containing a second rare earth element with aluminum oxidealong with the particle growth of the aluminum oxide by calcination inthe temperature range of 1,550° C. or more and 1,800° C. or less. Thus,the second crystal phase does not substantially contain an element thatcan be an activator, and the content of the element that can be anactivator is 200 ppm by mass or less. When the activating element of thefirst rare earth aluminate fluorescent material is cerium (Ce), thecontent of cerium (Ce) in the second crystal phase composed of thesecond rare earth aluminate is 200 ppm by mass or less. The content ofan element that can be an activator contained in the second crystalphase composed of the second rare earth aluminate can be determined bymeasuring the content of an element that can be an activator, forexample cerium, at the cross section of the second crystal phasecomposed of the second rare earth aluminate in the ceramic complex byenergy dispersive X-ray spectrometry (EDX). The content of an elementthat can be an activator contained in the second crystal phase composedof the second rare earth aluminate in the ceramic complex is 200 ppm bymass or less, and may be 150 ppm by mass or less, may be 100 ppm by massor less, may be the measurement limit by EDX or less, may be at 0 ppm bymass, may be 0.1 ppm by mass or more, or may be 1 ppm by mass or more.

The second rare earth aluminate preferably has a composition representedby the following formula (II). The second rare earth aluminate is formedby reacting the aluminum oxide particles with the oxide particlescontaining a second rare earth element by calcination in the temperaturerange of 1,550° C. or higher and 1,800° C. or lower, and when the secondrare earth element Ln² contained in the oxide particles is at least oneselected from the group consisting of Y, Gd, Tb, and Lu, the second rareearth element having a composition represented by the following formula(II) is formed:Ln² ₃Al₅O₁₂  (II)

wherein Ln² represents at least one element selected from the groupconsisting of Y, Gd, Tb, and Lu.

Ceramic Complex

The ceramic complex comprises a first crystal phase that contains afirst rare earth aluminate fluorescent material containing an activatingelement and a first rare earth element different from the activatingelement, a second crystal phase composed of a second rare earthaluminate containing a second rare earth element, wherein a content ofan element capable of being an activator in the second crystal phase is200 ppm by mass or less, and a third crystal phase composed of aluminumoxide, wherein the content of the first crystal phase is in a range of5% by volume or more and 45% by volume or less, the content of thesecond crystal phase is in a range of 0.5% by volume or more and 50% byvolume or less, and the content of the third crystal phase is thebalance, relative to 100% by volume of the total amount of the firstcrystal phase, the second crystal phase, and the third crystal phase.The ceramic complex is preferably produced by the above-mentionedproduction method. In the ceramic complex, the light emitted from theexcitation light source can be wavelength-converted by the first crystalphase containing the first rare earth aluminate fluorescent materialintegrated with the second rare earth aluminate contained in the rangeof 5% by volume or more and 45% by volume or less, allowing the ceramiccomplex to emit light with high luminance. Further, the ceramic complexcontains the second crystal phase composed of the second rare earthaluminate in the range of 0.5% by volume or more and 50% by volume orless, and the third crystal phase composed of aluminum oxide which isthe balance obtained by excluding the first crystal phase and the secondcrystal phase from 100% by volume of the first crystal phase, the secondcrystal phase, and the third crystal phase. Thus, the light is scatteredat the interface between the second crystal phase and the third crystalphase to increase the light absorption efficiency of the first crystalphase containing the first rare earth aluminate fluorescent materialintegrated with the second rare earth aluminate, and the wavelength canbe efficiently converted, allowing the ceramic complex to emit lightwith increased luminance. The content of the first crystal phase in theceramic complex may be in a range of 10% by volume or more and 40% byvolume or less, or may be in a range of 12% by volume or more and 35% byvolume or less. The content of the second crystal phase in the ceramiccomplex may be in a range of 1% by volume or more and 45% by volume orless, may be in a range of 3% by volume or more and 40% by volume orless, or may be in a range of 5% by volume or more and 35% by volume orless.

The content (% by volume) of the first crystal phase and the content (%by volume) of the second crystal phase in the ceramic complex can bedetermined by: photographing scanning electron microscope (SEM) imagesof several arbitrary cross sections of the ceramic complex using an SEM;determining volume ratios of the first crystal phase and the secondcrystal phase from the SEM images; and calculating the average valuefrom the volume ratios of the first crystal phase and the second crystalphase in the several arbitrary cross sections.

The content (% by volume) of the first crystal phase and the content (%by volume) of the second crystal phase in the ceramic complex can becalculated from: the content of mass ratio and true density of the firstrare earth aluminate fluorescent material particles; the content of massratio and true density of the oxide particles containing the second rareearth element; and the true density of the aluminum oxide particles inthe raw material mixture forming the ceramic complex.

Content (% by Volume) of First Crystal Phase

The content of the first crystal phase in the ceramic complex can becalculated based on the following formula (1):

$\begin{matrix}{{{First}\mspace{14mu}{crystal}\mspace{14mu}{{phase}\left( {\%\mspace{14mu}{by}\mspace{14mu}{volume}} \right)}} = {\frac{\left( {P\;{1_{m} \div P}\; 1_{d}} \right)}{\left( {P\;{1_{m} \div P}\; 1_{d}} \right) + \left\{ {{\left( {100 - {P\; 1_{m}}} \right) \div P}\; 3_{d}} \right\}} \times 100}} & (1)\end{matrix}$

-   -   Mass ratio (% by mass) of first crystal phase (first rare earth        aluminate fluorescent material particles): P1_(m)    -   True density (g/cm³) of first crystal phase (first rare earth        aluminate fluorescent material particles): P1_(d)    -   True density (g/cm³) of third crystal phase (aluminum oxide        particles); P3_(d)        Content (% by Volume) of Second Crystal Phase

The content of the second crystal phase in the ceramic complex can becalculated based on the following formula (2):

$\begin{matrix}{{{Second}\mspace{14mu}{crystal}\mspace{14mu}{{phase}\left( {\%\mspace{14mu}{by}\mspace{14mu}{volume}} \right)}} = {\frac{\left( {P\;{2_{m} \div P}\; 2_{d}} \right)}{\left( {P\;{2_{m} \div P}\; 2_{d}} \right) + \left\{ {{\left( {100 - {P\; 2_{m}}} \right) \div P}\; 3_{d}} \right\}} \times 100}} & (2)\end{matrix}$

-   -   Mass ratio (% by mass) of second crystal phase (second rare        earth aluminate): P2_(m)    -   True density (g/cm³) of second crystal phase (second rare earth        aluminate): P2_(d)    -   True density (g/cm³) of third crystal phase (aluminum oxide        particles): P3_(d)

The content (% by mass) of the mass ratio of the second crystal phase inthe ceramic complex can be calculated from the content (% by mass) ofthe mass ratio and true density of the oxide particles containing thesecond rare earth element in the raw material mixture, based on thefollowing formulae (3) and (4):

$\begin{matrix}{{{Second}\mspace{14mu}{crystal}\mspace{14mu}{{phase}\left( {\%\mspace{14mu}{by}\mspace{14mu}{volume}} \right)}\mspace{14mu}{Oxide}\mspace{14mu}{containing}\mspace{14mu}{second}\mspace{14mu}{rare}\mspace{14mu}{earth}\mspace{14mu}{element}} = {{in}\mspace{14mu}{raw}\mspace{14mu}{material}\mspace{14mu}{{mixture}\left( {\%\mspace{14mu}{by}\mspace{14mu}{mass}} \right)} \times K}} & (3)\end{matrix}$K=(Molecular weight of oxide containing second rare earth element÷Molarnumber of second rare earth element)×(Molecular weight of second rareearth aluminate÷Molar number of second rare earth element)  (4)

First Crystal Diameter G1 of First Crystal Phase and Second CrystalDiameter G2 of Second Crystal Phase

The first crystal phase and the second crystal phase contained in theceramic complex preferably have a first crystal diameter G1 of the firstcrystal phase in a range of 5 μm or more and 40 μm or less, and a secondcrystal diameter G2 of the second crystal phase in a range of 0.5 μm ormore and less than 5 μm, as measured under the following measurementconditions.

Measurement Conditions:

in a scanning electron microscope (SEM) image obtained by photographingthe cross section of the ceramic complex using an SEM, the maximum widthin the cross section of the first crystal phase or the second crystalphase, and the minimum width passing through the center point of themaximum width are measured; the average of the maximum width and theminimum width is defined as the diameter for each of the first crystalphase and the second crystal phase; and the average value of thediameters of 20 first crystal phases or second crystal phases randomlyselected is regarded as the first crystal diameter G1 of the firstcrystal phase or the second crystal diameter G2 of the second crystalphase.

When the first crystal diameter G1 of the first crystal phase containedin the ceramic complex falls within the range of 5 μm or more and 40 μmor less, the first crystal phase containing the first rare earthaluminate fluorescent material integrated with the second rare earthaluminate absorbs the light emitted from the excitation light source andconverts the wavelength, allowing the ceramic complex to emit light withhigh luminance. The first crystal diameter G1 of the first crystal phasemay be in a range of 8 μm or more and 35 μm or less, or may be in arange of 10 μm or more and 30 μm or less.

When the second crystal diameter G2 of the second crystal phasecontained in the ceramic complex falls within the range of 0.5 μm ormore and 5 μm or less, the light emitted from the excitation lightsource can be scattered at the interface between the second crystalphase composed of the second rare earth aluminate and the third crystalphase composed of aluminum oxide to enhance the light absorptionefficiency of the first crystal phase and efficiently convert thewavelength, allowing the ceramic complex to emit light with highluminance. The second crystal diameter G2 of the second crystal phasemay be in a range of 0.6 μm or more and 4 μm or less, or may be in arange of 0.7 μm or more and 3 μm or less.

Ratio G2/G1

The ratio G2/G1 of the second crystal diameter G2 to the first crystaldiameter G1 is preferably 0.4 or less, and may be 0.3 or less, may be0.2 or less, or may be 0.01 or more. When the ratio G2/G1 of the secondcrystal diameter G2 of the second crystal phase composed of the secondrare earth aluminate to the first crystal diameter G1 of the firstcrystal phase containing the first rare earth aluminate fluorescentmaterial integrated with the second rare earth aluminate is 0.4 or less,the first crystal phase becomes large compared to the second crystalphase, the absorption efficiency of the light emitted from theexcitation light source is improved, and the light emitted from theexcitation light source is efficiently absorbed andwavelength-converted, allowing the ceramic complex to emit light withhigher luminance. Further, when the ratio G2/G1 is 0.4 or less, thesecond crystal phase composed of the second rare earth aluminate becomessmall compared to the first crystal phase, the scattering of the lightemitted from the excitation light source at the interface between thesecond crystal phase and the third crystal phase is increased, and thelight absorption efficiency of the first crystal phase can be enhanced,allowing the ceramic complex to emit light with higher luminance. Theratio G2/G1 may be 0.3 or less, may be 0.2 or less, may be 0.01 or more,or may be 0.02 or more.

Relative Density

The ceramic complex preferably has a relative density of 95% or more.When the relative density of the ceramic complex is 95% or more, thescattering of the light emitted from the excitation light source at theinterface between the second crystal phase and the third crystal phasein the ceramic complex is increased, and the light emitted from theexcitation light source is efficiently absorbed in the first crystalphase and wavelength-converted, allowing the ceramic complex to emitlight with higher luminance. The relative density of the ceramic complexmay be 97% or more, or may be 98% or more.

The relative density of the ceramic complex can be calculated from theapparent density of the ceramic complex and the true density of theceramic complex by the following formula (5):Relative density (%) of ceramic complex=(Apparent density of ceramiccomplex÷True density of ceramic complex)×100  (5)

The apparent density of the ceramic complex is a value obtained bydividing the mass of the ceramic complex by the volume of the ceramiccomplex, and can be calculated by the following formula (6):Apparent density(g/cm³) of ceramic complex=Mass(g) of ceramiccomplex÷Volume(cm³) of ceramic complex(Archimedes' method)  (6)

The true density of the ceramic complex can be calculated by thefollowing formula (7):

$\begin{matrix}{{{True}\mspace{14mu}{{density}\left( \text{g/cm}^{3} \right)}\mspace{14mu}{of}\mspace{14mu}{ceramic}\mspace{14mu}{complex}} = \frac{{P\; 1_{m}} + {P\; 2_{m}} + {P\; 3_{m}}}{\left( {P\;{1_{m} \div P}\; 1_{d}} \right) + \left( {P\;{2_{m} \div P}\; 2_{d}} \right) + \left( {P\;{3_{m} \div P}\; 3_{d}} \right)}} & (7)\end{matrix}$

-   -   Mass ratio (% by mass) of first crystal phase (first rare earth        aluminate fluorescent material particles): P1_(m)    -   True density (g/cm³) of first crystal phase (first rare earth        aluminate fluorescent material particles): P1_(d)    -   Mass ratio (% by mass) of second crystal phase (second rare        earth aluminate): P2_(m)    -   True density (g/cm³) of second crystal phase (second rare earth        aluminate): P2_(d)    -   Mass ratio (% by mass) of third crystal phase (aluminum oxide        particles): P3_(m)    -   True density (g/cm³) of third crystal phase (aluminum oxide        particles): P3_(d) P1_(m)+P2_(m)+P3_(m)=100% by mass    -   wherein the content (% by mass) of the second crystal phase in        the ceramic complex can be calculated based on the above        formulae (3) and (4).

As for the sintered body, the first sintered body, and the secondsintered body obtained by the method for producing a ceramic complex,the relative density, the apparent density, and the true density can berespectively calculated by replacing the ceramic complex in the formulae(5) to (7) with the sintered body, the first sintered body, or thesecond sintered body.

The first rare earth aluminate fluorescent material contained in thefirst crystal phase of the ceramic complex preferably has a first rareearth aluminate composition that contains at least one first rare earthelement Ln¹ selected from the group consisting of Y, Lu, Gd, and Tb, Ceserving as the activating element, Al, and O (oxygen), and mayoptionally contain Ga, in which the total molar ratio of the first rareearth element Ln¹ and Ce is 3; the molar ratio of Ce is the product of aparameter a in a range of more than 0 and 0.22 or less, and 3; the totalmolar ratio of Al and Ga is in a range of 4.5 or more and 5.5 or less;the molar ratio of Al is the product of a parameter c in a range of morethan 0 and 1.1 or less, and 5; and the molar ratio of Ga that may beoptionally contained is the product of a parameter b in a range of 0 ormore and 0.4 or less, and 5. The composition of the first rare earthaluminate fluorescent material is preferably the same as that of thefirst rare earth aluminate fluorescent material contained in the rawmaterial mixture. By containing the first rare earth aluminatefluorescent material in the first crystal phase of the ceramic complex,the light emitted from the excitation light source iswavelength-converted and can be emitted from the ceramic complex. Thefirst rare earth aluminate fluorescent material contained in the firstcrystal phase of the ceramic complex preferably has a compositionrepresented by the above formula (I).

The second rare earth aluminate constituting the second crystal phase ofthe ceramic complex may contain at least one second rare earth elementselected from the group consisting of Y, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb,Dy, Ho, Er, Tm, Yb, and Lu. The second rare earth aluminate preferablycontains at least one second rare earth element Ln² selected from thegroup consisting of Y, Gd, Tb, and Lu. The second rare earth aluminatepreferably has a second rare earth aluminate composition that containsat least one second rare earth element Ln² selected from the groupconsisting of Y, Gd, Tb, and Lu, and Al, in which the molar ratio of thesecond rare earth element Ln² is 3 and the molar ratio of Al is 5. Thisis because the second rare earth aluminate having the composition can beeasily integrated with the first rare earth aluminate fluorescentmaterial, and the first crystal diameter of the first crystal phase canbe increased. The second rare earth aluminate constituting the secondcrystal phase contained in the ceramic complex preferably has acomposition represented by the above formula (II) since it is easilyintegrated with the first rare earth aluminate fluorescent material. Thesecond crystal phase composed of the second rare earth aluminatesubstantially does not contain an element that can be an activator; andthe content of an element that can be an activator in the second crystalphase is 200 ppm by mass or less, and may be 150 ppm by mass or less,may be 100 ppm by mass or less, may be the above-mentioned measurementlimit by EDX or less, may be at 0 ppm by mass, may be 0.1 ppm by mass ormore, or may be 1 ppm by mass or more. When the activating element ofthe first rare earth aluminate fluorescent material is cerium (Ce), thecontent of cerium (Ce) in the second crystal phase composed of thesecond rare earth aluminate is 200 ppm by mass or less.

Light Emitting Device

The ceramic complex can be used as a member constituting a wavelengthconversion member of a light emitting device in combination with a lightsource. An example of a light emitting device using the ceramic complexwill be described.

The light emitting device comprises a wavelength conversion memberincluding a ceramic complex, and an excitation light source.

FIG. 3A shows an exemplary light emitting device and is a schematic planview of a light emitting device 100; and FIG. 3B is a schematiccross-sectional view of the IIIB-IIIB′ line of the light emitting device100 shown in FIG. 3A. The light emitting device 100 includes a lightemitting element 20 composed of an LED or LD, and a wavelengthconversion member 30 composed of a ceramic complex that is excited bylight emitted from the light emitting element 20 to emit light. Thelight emitting element 20 is flip-chip mounted on a substrate 10 viabumps which are conductive members 60. The wavelength conversion member30 is arranged on the light emitting surface of the light emittingelement 20 via an adhesive layer 40. The side surfaces of the lightemitting element 20 and the wavelength conversion member 30 are coveredwith a covering member 50 that reflects light. The light emittingelement 20 receives electric power from the outside of the lightemitting device 100 via wiring and the conductive members 60 formed onthe substrate 10, so that the light emitting device 100 is able to emitlight. The light emitting device 100 may include a semiconductor element70 such as a protective element for preventing the light emittingelement 20 from being destroyed by applying an excessive voltage. Thecovering member 50 is provided so as to cover, for example, thesemiconductor element 70. The covering member 50 may include a resin 51and at least one additive material 52 selected from the group consistingof a colorant, a fluorescent material, and a filler. Each member used inthe light emitting device will be hereunder described. For the details,for example, the disclosure of Japanese Unexamined Patent PublicationNo. 2014-112635 may be referred to.

Light Emitting Element

As the light emitting element, for example, an LED chip or LD chip,which is a semiconductor light emitting element using a nitride-basedsemiconductor, can be used

The light emitting element preferably has a light emission peakwavelength in a range of 380 nm or more and 500 nm or less, morepreferably in a range of 390 nm or more and 495 nm or less, even morepreferably in a range of 400 nm or more and 490 nm or less, andparticularly preferably in a range of 420 nm or more and 490 nm or less.The light emitting element is provided with a p-electrode and ann-electrode. The p-electrode and the n-electrode of the light emittingelement may be formed on the same side surface as the light emittingelement, or may be provided on different side surfaces. The lightemitting element may be flip-chip mounted.

Wavelength Conversion Member

As the wavelength conversion member, the above-mentioned ceramic complexcan be used. The thickness of the ceramic complex used as the wavelengthconversion member may be in a range of 50 μm or more and 500 μm or less,may be in a range of 60 μm or more and 450 μm or less, or may be in arange of 70 μm or more and 400 μm or less. The size of the ceramiccomplex used as the wavelength conversion member may be a size capableof covering the entire light-extracting surface of the light emittingelement. There may be an adhesive layer interposed between the lightemitting element and the wavelength conversion member, and the lightemitting element and the wavelength conversion member may be adhered bythe adhesive layer. The adhesive constituting the adhesive layer ispreferably made of a material capable of optically connecting the lightemitting element and the wavelength conversion member. The materialconstituting the adhesive layer is preferably at least one resinselected from the group consisting of an epoxy resin, a silicone resin,a phenol resin, and a polyimide resin.

Substrate

The substrate is preferably made of an insulating material that is hardto transmit light from the light emitting element and external light.Examples of the material of the substrate include ceramics such asaluminum oxide and aluminum nitride, and resins such as a phenol resin,an epoxy resin, a polyimide resin, a bismaleimide triazine resin (BTresin), and a polyphthalamide (PPA) resin. Ceramics have high heatresistance and are thus preferable as a substrate material.

Adhesive Layer

The adhesive layer is interposed between the light emitting element andthe wavelength conversion member to adhere the light emitting elementand the wavelength conversion member together. The adhesive constitutingthe adhesive layer is preferably made of a material capable of opticallyconnecting the light emitting element and the wavelength conversionmember. The material constituting the adhesive layer is preferably atleast one resin selected from the group consisting of an epoxy resin, asilicone resin, a phenol resin, and a polyimide resin.

Semiconductor Element

Examples of the semiconductor element optionally provided in the lightemitting device include a transistor for controlling the light emittingelement and a protective element for suppressing the destruction and theperformance deterioration of the light emitting element due to excessivevoltage application. Examples of the protective element include a Zenerdiode and a capacitor.

Covering Member

As the material of the covering member, an insulating material ispreferably used. More specific examples thereof include a phenol resin,an epoxy resin, a bismaleimide triazine resin (BT resin), apolyphthalamide (PPA) resin, and a silicone resin. The covering membermay optionally include at least one additive material selected from thegroup consisting of a colorant, a fluorescent material, and a filler.

Conductive Member

As the conductive member, a bump can be used. Examples of the materialof the bump include Au and an alloy thereof, and examples of the otherconductive member include eutectic solder (Au—Sn), Pb—Sn, and lead-freesolder.

Method for Producing Light Emitting Device

An example of the method for producing a light emitting device will bedescribed. For the details, for example, the disclosure of JapaneseUnexamined Patent Publication No. 2014-112635 or Japanese UnexaminedPatent Publication No. 2017-117912 may be referred to. The method forproducing a light emitting device preferably includes a step ofarranging a light emitting element, optionally a step of arranging asemiconductor element, a step of forming a wavelength conversion memberincluding a ceramic complex, a step of adhering a light emitting elementand a wavelength conversion member, and a step of forming a coveringmember.

Step of Arranging Light Emitting Element

In the step of arranging a light emitting element, the light emittingelement is arranged and mounted on the substrate. For example, the lightemitting element and the semiconductor element are flip-chip mounted onthe substrate.

Step of Adhering Light Emitting Element and Wavelength Conversion Member

In the step of adhering a light emitting element and a wavelengthconversion member, the wavelength conversion member is opposed to thelight emitting surface of the light emitting element, and the wavelengthconversion member is adhered onto the light emitting element by theadhesive layer.

Step of Forming Covering Member

In the step of forming a covering member, the side surfaces of the lightemitting element and the wavelength conversion member excluding thelight emitting surface are covered with the composition for a coveringmember, and the covering member is formed on the side surfaces of thelight emitting element and the wavelength conversion member excludingthe light emitting surface. The covering member is for reflecting lightemitted from the light emitting element, and is formed so as to coverthe side surfaces without covering the light emitting surface of thewavelength conversion member and to embed the semiconductor element.

As described above, the light emitting device shown in FIGS. 3A and 3Bcan be produced.

EXAMPLES

The present disclosure is hereunder specifically described by referenceto the following Examples. The present disclosure is not limited tothese Examples.

Example 1

Step of Preparing Raw Material Mixture

A first rare earth aluminate fluorescent material having a compositionof (Y_(0.893)Gd_(0.10)Ce_(0.007))₃Al₅O₁₂ containing Ce as the activatingelement, and Y and Gd as the first rare earth elements was prepared. Thefirst average particle diameter D1 of the first rare earth aluminatefluorescent material particles according to the FSSS method was 10 μm.

Yttrium oxide (Y₂O₃) containing Y as the second rare earth element wasprepared. The second average particle diameter D2 of the yttrium oxideparticles, which were the oxide particles containing the second rareearth element, according to the FSSS method was 0.1 μm.

As the aluminum oxide particles, aluminum oxide (Al₂O₃) having a purityof aluminum oxide of 99% by mass was prepared. The third averageparticle diameter D3 of the aluminum oxide particles according to theFSSS method was 0.6 μm.

Next, 14 g of the first rare earth aluminate fluorescent material, 0.5 gof the yttrium oxide particles, and 85.5 g of the aluminum oxideparticles were respectively weighed and mixed using a dry-type ballmill, and balls as mixing media were removed, thereby preparing a rawmaterial mixture. The content of each of the particles relative to 100%by mass of the raw material mixture composed of the total of the firstrare earth aluminate fluorescent material particles, the yttrium oxideparticles, and the aluminum oxide particles, is shown in Table 1.

Step of Preparing Molded Body

The raw material mixture was charged in a die to form a cylindricalmolded body having a diameter of 65 mm and a thickness of 15 mm at apressure of 5 MPa (51 kgf/cm²). The obtained cylindrical molded body wasplaced in a packaging container and vacuum-packed, and subjected to coldisostatic pressing (CIP) at 176 MPa using a CIP apparatus (manufacturedby Kobe Steel, Ltd. (KOBELCO)) to obtain a molded body.

Step of Obtaining Sintered Body

Primary Calcining Step

The obtained molded body was primarily calcined at a temperature of1,650° C. in an air atmosphere (0.101 MPa, oxygen concentration of 20%by volume) using a calcining furnace (manufactured by Marusho Denki Co.,Ltd.) to obtain a first sintered body.

Secondary Calcining Step

The obtained first sintered body was secondarily calcined by hotisostatic pressing (HIP) at a temperature of 1,650° C. and a pressure of195 MPa for 2 hours under a nitrogen gas atmosphere (99.99% by volume ormore) using nitrogen gas as a pressure medium, by using a HIP apparatus(manufactured by Kobe Steel, Ltd. (KOBELCO)) to obtain a second sinteredbody. The second sintered body was cut into a predetermined shape andsize using a wire saw, and the surface of the cut section was polishedusing a surface grinder, thereby obtaining a plate-shaped ceramiccomplex of Example 1 having a thickness of 180 μm. In the ceramiccomplex of Example 1, along with the particle growth of the aluminumoxide particles, the second crystal phase composed of the second rareearth aluminate represented by Y₃Al₅O₁₂, which was formed by reactingthe aluminum oxide particles with the yttrium oxide particles, wasformed. The content of Ce in the second crystal phase of the crosssection of the ceramic complex was measured using a wavelengthdispersion-type X-ray analysis EPMA (WDS) apparatus (JXA-8230,manufactured by JEOL Ltd.). As a result, the content of Ce was 100 ppmby mass or less.

Examples 2 to 5

A ceramic complex in each of Examples 2 to 5 was obtained in the samemanner as in Example 1 except that the contents of the yttrium oxideparticles and the aluminum oxide particles contained in the raw materialmixture were changed as shown in Table 1.

Example 6

A first rare earth aluminate fluorescent material having a compositionof (Y_(0.940)Gd_(0.05)Ce_(0.010))₃Al₅O₁₂ containing Ce as the activatingelement, and Y and Gd as the first rare earth elements was prepared. Thefirst average particle diameter D1 of the first rare earth aluminatefluorescent material particles according to the FSSS method was 15 μm.Using the above first rare earth aluminate fluorescent material and thesame yttrium oxide particles and aluminum oxide particles as in Example1, 10.5 g of the first rare earth aluminate fluorescent material, 10 gof the yttrium oxide particles, and 9.57 g of the aluminum oxideparticles were respectively weighed, and a raw material mixture wasprepared in the same manner as in Example 1. The content of each of theparticles relative to 100% by mass of the raw material mixture composedof the total of the first rare earth aluminate fluorescent materialparticles, the yttrium oxide particles, and the aluminum oxideparticles, is shown in Table 1. A ceramic complex of Example 6 wasobtained in the same manner as in Example 1 except that the above rawmaterial mixture was used. In the ceramic complex of Example 6, alongwith the particle growth of the aluminum oxide particles, the secondcrystal phase composed of the second rare earth aluminate represented byY₃Al₅O₁₂, which was formed by reacting the aluminum oxide particles withthe yttrium oxide particles, was formed. The content of Ce in the secondcrystal phase of the cross section of the ceramic complex was measuredusing the above-mentioned wavelength dispersion-type X-ray analysis EPMA(WDS) apparatus. As a result, the content of Ce was 100 ppm by mass orless.

Comparative Example 1

A ceramic complex of Comparative Example 1 was obtained in the samemanner as in Example 1 except that a raw material mixture containing 86g of the aluminum oxide particles and no yttrium oxide particles wasused.

Comparative Example 2

A ceramic complex of Comparative Example 2 was obtained in the samemanner as in Example 6 except that a raw material mixture containing89.5 g of the aluminum oxide particles and no yttrium oxide particleswas used.

Particle Diameter Measurement

The average particle diameter of each of the first rare earth aluminatefluorescent material particles, the oxide particles, and the aluminumoxide particles was measured as follows.

As for each of the particles, using a Fisher Sub-Sieve Sizer Model 95(manufactured by Fisher Scientific Inc.) under an environment of atemperature of 25° C. and a relative humidity of 70%, 1 cm³ of theparticles (raw material sample) was weighed and packed in a dedicatedtubular container, followed by flowing dry air at a constant pressure,and the specific surface area was read from the differential pressure tocalculate the average particle diameter according to the FSSS method.The results are as described above.

Using the obtained ceramic complex in each of Examples and ComparativeExamples, the light emitting device 100 shown in FIGS. 3A and 3B wasproduced as follows. The light emitting element 20 and the semiconductorelement 70 were mounted on the mounting substrate 10. Specifically, thelight emitting element 20 having a thickness of about 0.11 mm, asubstantially square planar shape of about 1.0 mm square, and a dominantwavelength of 450 nm, which was formed by laminating a nitridesemiconductor on a sapphire substrate, and the semiconductor element 70were arranged in line such that the side of the sapphire substrateserving as a semiconductor growth substrate faced the light emittingsurface; and these were flip-chip mounted on the conductive patternformed on the mounting substrate 10 by using the conductive members 60composed of Au.

Next, a silicone resin serving as the adhesive layer 40 was arranged onthe upper surface of the light emitting element 20, and the wavelengthconversion member 30 obtained by forming the ceramic complex in each ofExamples and Comparative Examples into a plate shape was adhered to theupper surface of the sapphire substrate of the light emitting element20.

Next, the covering member 50 was arranged around the light emittingelement 20, the wavelength conversion member 30, and the semiconductorelement 70. The covering member 50 was arranged along the side surfacesof the light emitting element 20 and the wavelength conversion member30, and the semiconductor element 70 was completely embedded in thecovering member 50. A dimethyl silicone resin was used as the resin 51contained in the covering member 50, and titanium oxide particles havingan average particle diameter of 0.28 μm serving as the light-reflectingmaterial 52 was contained in the covering member 50 in an amount of 60%by mass relative to the resin 51. Through such steps, the light emittingdevice 100 shown in FIGS. 3A and 3B was produced.

The light emitting device using the ceramic complex in each of Examplesand Comparative Examples was evaluated as follows. The results are shownin Table 1.

Relative Luminance and Chromaticity Coordinates (x, y)

For the ceramic complex in each of Examples and Comparative Examples,the luminance and the chromaticity coordinates (x, y) in thechromaticity coordinate system of the Commission Internationale del'Eclairage (CIE) 1931 chromaticity diagram were determined using animaging color luminance meter (ProMetric I8, manufactured by RadiantVision Systems, LLC). The relative luminance was determined from therelative value of the luminance of the ceramic complex in each ofExamples and Comparative Examples when the luminance of the ceramiccomplex of Comparative Example 1 was defined as 100%. FIG. 4 is a graphdescribing a relationship between the content of the yttrium oxideparticles in the raw material mixture used in each ceramic complex andthe relative luminance of each ceramic complex obtained from the rawmaterial mixture.

Contents of First Crystal Phase and Second Crystal Phase

The content of the first crystal phase (% by volume) and the content ofthe second crystal phase (% by volume and % by mass) were determinedbased on the above formulae (1) to (4).

Relative Density

The relative density of the ceramic complex in each of Examples andComparative Examples was determined based on the above formulae (5) to(7). In the formula (7), the true density of the ceramic complex wascalculated as the true density of the first rare earth aluminatefluorescent material ((Y_(0.940)Gd_(0.05)Ce_(0.010))₃Al₅O₁₂) was 4.73g/cm³, the true density of the aluminum oxide (Al₂O₃) particles was 3.98g/cm³, and the true density of the second rare earth aluminate(Y₃Al₅O₁₂) was 4.60 g/cm³.

SEM Image—Secondary Electron Image

Using a scanning electron microscope (SEM) (SU3500, manufactured byHitachi High-Technologies Corp.), an SEM photograph of a secondaryelectron image in the cross section (polished surface) of the ceramiccomplex in each of Examples and Comparative Examples was obtained. FIG.5 shows an SEM photograph of the secondary electron image in the crosssection (polished surface) of the ceramic complex in Example 3.

Crystal Diameter

The first crystal diameter G1 of the first crystal phase containing thefirst rare earth aluminate fluorescent material, the second crystaldiameter G2 of the second crystal phase composed of the second rareearth aluminate, and the ratio G2/G1 were measured from the SEMphotograph of the polished cross sectional surface of the ceramiccomplex in each of Examples and Comparative Examples under the followingmeasurement conditions.

Measurement Conditions:

in an SEM image of the cross section of the ceramic complex, the maximumwidth in the cross section of the first crystal phase or the secondcrystal phase, and the minimum width passing through the center point ofthe maximum width were measured; the average of the maximum width andthe minimum width was defined as the diameter for each of the firstcrystal phase and the second crystal phase; and the average value of thediameters of 20 first crystal phases or second crystal phases randomlyselected was regarded as the first crystal diameter G1 of the firstcrystal phase or the second crystal diameter G2 of the second crystalphase.

SEM Image—Reflected Electron Image

Using a field emission scanning electron microscope (FE-EM) (JSM-7800F,manufactured by JEOL Ltd.), an SEM photograph of a reflected electronimage in the cross section (polished surface) of the ceramic complex ineach of Examples and Comparative Examples was obtained. FIG. 6 shows anSEM photograph of the reflected electron image in the cross section(polished surface) of the ceramic complex in Example 3.

TABLE 1 Raw material mixture First rare earth Ceramic complex aluminateAluminum First Second Second First Second fluorescent Oxide oxidecrystal crystal crystal crystal crystal Particle material particlesparticles phase phase phase diameter diameter diameter RelativeChromaticity Relative particles (% by (% by (% by (% by (% by G1 G2ratio density coordinates luminance (% by mass) mass) mass) volume)mass) volume) (μm) (μm) G2/G1 (%) x y (%) Example 1 14.0 0.5 85.5 12.00.9 0.8 10.1 1.2 0.1 99.9 0.315 0.322 100.8 Example 2 14.0 5.0 81.0 12.08.8 7.7 10.3 1.0 0.1 99.8 0.316 0.324 101.3 Example 3 14.0 10.0 76.012.0 17.5 15.5 10.6 1.1 0.1 99.7 0.324 0.340 101.5 Example 4 14.0 20.066.0 12.0 35.1 31.8 11.0 2.1 0.2 99.4 0.330 0.352 101.9 Example 5 14.030.0 56.0 12.0 52.6 49.0 10.8 2.8 0.3 99.2 0.326 0.344 100.6 Example 610.5 10.0 79.5 9.0 17.5 15.5 14.6 1.1 0.1 99.9 0.322 0.336 101.9Comparative 14.0 0.0 86.0 12.0 0.0 0.0 10.5 — — 99.9 0.315 0.320 100.0Example 1 Comparative 10.5 0.0 89.5 9.0 0.0 0.0 15.2 — — 100.0 0.3130.316 100.0 Example 2

The ceramic complex according to each of Examples 1 to 6 had higherrelative luminance than that of the ceramic complex according each ofComparative Examples 1 and 2. It is presumed that the first crystaldiameter G1 of the first crystal phase containing the first rare earthaluminate fluorescent material in the ceramic complex according to eachof Examples 1 to 6 was larger than the first crystal diameter G1 of thefirst crystal phase composed of the first rare earth aluminatefluorescent material in the ceramic complex according to each ofComparative Examples 1 and 2, and thus a part of the second rare earthaluminate formed by reacting the oxide particles with the aluminum oxidewas integrated with the first rare earth aluminate fluorescent materialto form the first crystal phase containing the first rare earthaluminate fluorescent material. It is presumed that the ceramic complexaccording to each of Examples 1 to 6 had a larger first crystal diameterG1 of the first crystal phase, and thus the light emitted from theexcitation light source was easily wavelength-converted and the relativeluminance was enhanced. In addition, the ceramic complex according toeach of Examples 1 to 6 contained the second crystal phase composed ofthe second rare earth aluminate by reacting the oxide particles with thealuminum oxide particles, so that the light could be scattered at theinterface between the second crystal phase and the third crystal phasecomposed of the aluminum oxide particles and emitted to the outside ofthe ceramic complex, and the absorption of light in the first crystalphase containing the first rare earth aluminate fluorescent materialcould be enhanced to increase the wavelength conversion efficiency oflight, resulting that the relative luminance was higher than that of theceramic complex according to each of Comparative Examples 1 and 2.

As shown in FIG. 4 , when the content of the first rare earth aluminatefluorescent material particles was in the range of 5% by mass or moreand 40% by mass or less, the content of the oxide particles was in therange of 0.1% by mass or more and 32% by mass or less, and the contentof the aluminum oxide particles was the balance, relative to 100% bymass of the total amount of the first rare earth aluminate fluorescentmaterial particles, the oxide particles, and the aluminum oxideparticles in the raw material mixture, the relative luminance of theceramic complex obtained from such a raw material mixture was higherthan that of the ceramic complex having an oxide particle contentoutside the above range. In particular, the ceramic complex according toeach of Examples 1 to 4, which were obtained from the raw materialmixture with the content of the oxide particles in a range of 3.0% bymass or more and 25% by mass or less, had a higher relative luminancethan that of the ceramic complex according to each of ComparativeExamples 1 and 2 by 1% or more.

As shown in the secondary electron image of the ceramic complexaccording to Example 3 shown in FIG. 5 and the reflected electron imageof the ceramic complex according to Example 3 shown in FIG. 6 , thefirst crystal phase 1 containing the first rare earth aluminatefluorescent material, the second crystal phase 2 composed of the secondrare earth aluminate, and the third crystal phase 3 composed of thealuminum oxide particles were observed in the ceramic complex. A clearinterface was observed between the second crystal phase 2 and the thirdcrystal phase 3. It is presumed that, since the first crystal diameterG1 of the first crystal phase 1 of the ceramic complex according to eachof Examples 1 to 6 was larger than that of the first crystal phase 1 ofthe ceramic complex according to each of Comparative Examples 1 and 2,the first rare earth aluminate fluorescent material was integrated withthe second rare earth aluminate formed by reacting the oxide particleswith the aluminum oxide. In the first crystal phase 1, no interface wasobserved between the first rare earth aluminate fluorescent material andthe second rare earth aluminate, and it was observed that they wereintegrated.

The ceramic complex obtained by the method for producing a ceramiccomplex according to the embodiment of the present disclosure can beused as a wavelength conversion member for various applications such asan on-vehicle light source, an illumination device for general lighting,a backlight of a liquid crystal display device, and a light source for aprojector, in combination with an excitation light source such as an LEDor LD.

The invention claimed is:
 1. A ceramic complex, comprising a firstcrystal phase that contains a first rare earth aluminate fluorescentmaterial containing an activating element and a first rare earth elementdifferent from the activating element, a second crystal phase comprisinga second rare earth aluminate containing a second rare earth element,wherein a content of an element capable of being an activator in thesecond crystal phase is 200 ppm by mass or less, and a third crystalphase comprising aluminum oxide, wherein a content of the first crystalphase is in a range of 5% by volume or more and 45% by volume or less, acontent of the second crystal phase is in a range of 0.5% by volume ormore and 50% by volume or less, and a content of the third crystal phaseis the balance, relative to 100% by volume of a total amount of thefirst crystal phase, the second crystal phase, and the third crystalphase, and wherein a first crystal diameter G1 of the first crystalphase is in a range of 5 μm or more and 40 μm or less, and a secondcrystal diameter G2 of the second crystal phase is in a range of 0.5 μmor more and less than 5 μm, as measured under the following measurementconditions: in a scanning electron microscope (SEM) image obtained byphotographing a cross section of the ceramic complex using an SEM, themaximum width in the cross section of the first crystal phase or thesecond crystal phase, and the minimum width passing through a centerpoint of the maximum width are measured; an average of the maximum widthand the minimum width is defined as a diameter for each of the firstcrystal phase and the second crystal phase; and an average value of thediameters of 20 first crystal phases or second crystal phases randomlyselected is regarded as the first crystal diameter G1 of the firstcrystal phase or the second crystal diameter G2 of the second crystalphase.
 2. The ceramic complex according to claim 1, wherein a ratioG2/G1 of the second crystal diameter G2 to the first crystal diameter G1is 0.4 or less.
 3. The ceramic complex according to claim 1, having arelative density that is 95% or more.
 4. The ceramic complex accordingto claim 1, wherein the first rare earth aluminate fluorescent materialhas a first rare earth aluminate composition that contains at least onefirst rare earth element Ln¹ selected from the group consisting of Y,Lu, Gd, and Tb, Ce serving as the activating element, Al, and O(oxygen), and optionally contains Ga, wherein the total molar ratio ofthe first rare earth element Ln¹ and Ce is 3; the molar ratio of Ce isthe product of 3 and a parameter a, where the parameter a is in a rangeof more than 0 and 0.22 or less; the total molar ratio of Al and Ga isin a range of 4.5 or more and 5.5 or less; the molar ratio of Al is theproduct of 5 and a parameter c, where the parameter c is in a range ofmore than 0 and 1.1 or less; and the molar ratio of Ga is the product of5 and a parameter b, where the parameter b is in a range of 0 or moreand 0.4 or less.
 5. The ceramic complex according to claim 1, whereinthe first rare earth aluminate fluorescent material has a compositionrepresented by the following formula (I):(Ln¹ _(1-a)Ce_(a))₃(Al_(c)Ga_(b))₅O₁₂  (I) wherein Ln¹ represents atleast one element selected from the group consisting of Y, Gd, Lu, andTb; and the parameters a, b, and c each satisfy 0<a≤0.22, 0≤b≤0.4,0<c≤1.1, and 0.9≤b+c≤1.1.
 6. The ceramic complex according to claim 1,wherein the second rare earth aluminate has a second rare earthaluminate composition that contains at least one second rare earthelement Ln² selected from the group consisting of Y, Gd, Tb, and Lu, andAl, wherein a molar ratio of the second rare earth element Ln² is 3 anda molar ratio of Al is
 5. 7. The ceramic complex according to claim 1,wherein the second rare earth aluminate has a composition represented bythe following formula (II):Ln² ₃Al₅O₁₂  (II) wherein Ln² represents at least one selected from thegroup consisting of Y, Gd, Tb, and Lu.